I was 10 or 11 when I first tried a brush handle. No big deal, as long as you're not hurting yourself with it. Go slow, and if you like it then you're fine. If you don't like it, find a different way to masturbate.
As long as you start out slow and make sure you don't hurt yourself, any age is fine to masturbate.
I started with a hairbrush handle at around 11/12, and I still use a hairbrush handle, heh.
It's good and discrete, since it's not embarrassing if someone finds a hairbrush in your room, and I like that.